But holding a phone number is not the same as being able to reach the customer.
Some numbers are wrong. Some are inactive. Some are landlines. Some are duplicated. Some have changed hands. Some were entered years ago and have never been checked.
That gap between the numbers a business holds and the people it can actually reach is what we call the Contactability Gap.
It is a simple idea, but it can have a real business impact.
When businesses rely on poor phone number data, messages fail, teams spend more time chasing, customer journeys break, and money is wasted trying to contact people who cannot be reached.
What do we mean by contactability?
Contactability is the ability to reach a customer using the contact data your business holds.
For phone numbers, that means more than checking whether a number looks right.
A contactable number should be valid, correctly formatted, suitable for the message being sent, and likely to reach the right person.
That matters because many important customer journeys depend on phone numbers.
- A delivery update only works if it reaches the customer.
- A one-time passcode only works if it arrives on the right phone.
- An appointment reminder only works if the number is still active.
- A claims update only works if the policyholder can actually receive it.
If the number behind the message is wrong, the journey starts to fail before the message has even been sent.
What is the Contactability Gap?
The Contactability Gap is the difference between the phone numbers in your systems and the customers you can actually reach.
For example, a business may hold 500,000 customer phone numbers. On paper, that looks like 500,000 contactable customers, whereas in reality, some of those numbers may no longer work.
Some may belong to a different person. Some may be landlines. Some may be stored in the wrong format. Some may be duplicated across different records. Some may not be suitable for SMS, verification or urgent customer updates.
The business still has the data, but it does not have the same level of contactability.
That is the gap.
Why phone numbers become unreliable
Phone number data changes all the time.
Customers change numbers. They switch networks. They move countries. They mistype details. They abandon accounts. They update one system but not another.
Businesses also collect phone numbers in lots of different places. A number might come from a checkout form, a call centre, a sales team, a mobile app, a customer portal, a spreadsheet, an old CRM record or a third-party integration.
Over time, small issues build up.
A number entered incorrectly at sign-up may sit in a database for years. A duplicated record may receive the same message twice. A landline may be stored where a mobile number is needed. An old number may still be used for important account communication.
None of this is unusual; it is what happens when customer data is collected once but used many times.
Why this matters to your business
Poor phone number data creates problems that are easy to miss.
- A failed SMS may look like a delivery issue.
- A missed appointment may look like customer behaviour.
- A support ticket may look like a service problem.
- A campaign may look like it simply underperformed.
But sometimes the problem started earlier; the number was not reliable enough in the first place, and when that happens at scale, poor contactability can create four common business problems.
1. Wasted communication spend
Messages sent to invalid, inactive or duplicated numbers still create cost.
One failed message may not feel significant. But across thousands or millions of customer records, the waste adds up quickly.
This is especially important for businesses sending regular SMS updates, marketing campaigns, reminders, alerts or verification messages.
If the number cannot be reached, the spend is already weakened.
2. Broken customer journeys
Phone numbers often sit behind important customer moments.
They support checkout, account access, delivery updates, claims communication, appointment reminders, service alerts and customer support.
When the number is wrong, those journeys become harder for everyone.
The customer may not receive the update. The business may not know the message failed. The support team may have to step in manually. The experience becomes slower, messier and more frustrating than it needs to be.
3. More manual chasing
When automated communication fails, people usually pick up the work.
Customer service teams resend information. Operations teams make follow-up calls. Claims handlers chase updates. Lettings teams confirm appointments manually. Delivery teams deal with avoidable “where is my order?” queries.
Poor contactability does not just affect messaging performance; it creates extra work.
4. More risk
Some customer journeys need more confidence than others.
A one-time passcode, fraud check, claims update, account alert or payment-related message depends on the business having enough trust in the number being used.
If phone data is outdated, duplicated, reassigned or unsuitable, it can create avoidable risk.
This does not mean every poor-quality number is dangerous.
It means businesses need better visibility before relying on phone numbers for important communication.
Where the Contactability Gap shows up
The Contactability Gap is not limited to one type of business.
It appears wherever customer phone numbers are used to support important journeys.
Retail and eCommerce
Retailers rely on phone numbers for delivery updates, loyalty campaigns, abandoned basket messages, click-and-collect alerts, customer service and one-time passcodes.
If phone data is poor, customers may miss updates, campaigns may underperform, and support teams may receive more avoidable queries.
Couriers and delivery platforms
Delivery businesses need accurate customer contact details to keep orders, drivers, riders and support teams aligned.
When numbers are wrong or inactive, ETA updates can fail, delivery attempts can become harder to complete, and customer support demand can increase.
Insurance
Insurers rely on phone numbers for claims updates, renewal reminders, fraud-sensitive journeys, customer service and vulnerable customer communication.
If the contact data is unreliable, teams may spend more time chasing customers and less time moving cases forward.
Estate and letting agents
Property teams use phone numbers for viewing reminders, tenant updates, landlord communication, maintenance appointments, referencing and arrears activity.
When contact data is poor, no-shows, delays and manual chasing become more likely.
Credit and collections
Credit, referencing and collections teams often depend on accurate contact data to verify applicants, support decisioning and maintain communication.
Poor contactability can slow processes, increase manual work and weaken customer engagement.
How to start closing the gap
Closing the Contactability Gap starts with asking better questions.
Not just:
“Do we have a phone number?”
But:
- Is the number valid?
- Is it correctly formatted?
- Is it active?
- Is it a mobile number?
- Is it suitable for the message we want to send?
- Is it duplicated across records?
- Has it been checked recently?
- Which customer journeys depend on it?
- What happens when this number cannot be reached?
These questions help businesses move away from guesswork.
Instead of simply sending more messages and hoping they work, teams can understand which numbers are reliable, which records need attention, and where failed contact may be creating unnecessary cost.
What businesses can do next?
There are several practical steps businesses can take.
Clean the data you already hold
Start by reviewing the phone numbers in your CRM, customer platform or operational systems. Look for obvious formatting problems, duplicates, missing country codes, landlines where mobile numbers are needed, and old records that have not been checked recently.
Validate before important journeys
Some journeys matter more than others. A delivery update, OTP, appointment reminder, claims message or account alert should not rely on unchecked data.
Validating numbers before key journeys helps reduce avoidable failure.
Review where failed contact creates work
Look at the places where teams spend time chasing customers manually.
If the same issues keep appearing, poor contactability may be part of the reason.
Measure the cost of failed contact
The cost is not only the failed message.
It may include support time, delayed journeys, missed appointments, failed deliveries, duplicated outreach, customer complaints and lower trust.
Once the cost is visible, it becomes easier to fix.
How Acudo helps
Acudo helps businesses validate, verify and improve customer phone number data before they communicate. That means teams can better understand whether numbers are correctly formatted, active, suitable and useful before relying on them for SMS, one-time passcodes, service alerts, customer updates or operational workflows. The aim is simple. Help businesses reduce failed contact, improve customer data quality and communicate with more confidence. If your business depends on customer phone numbers, a Contactability Health Check can help you understand where poor phone data may be creating wasted spend, failed journeys or avoidable manual work.
FAQs
What is contactability?
Contactability is the ability to reach a customer using the contact data your business holds. For phone numbers, this means understanding whether a number is valid, suitable and likely to reach the right person.
What is the Contactability Gap?
The Contactability Gap is the difference between the phone numbers a business holds and the customers it can actually reach.
Why do phone numbers become unreliable?
Phone numbers become unreliable when customers change numbers, records become outdated, numbers are entered incorrectly, data is duplicated, or systems are not checked regularly.
Why does phone number validation matter?
Phone number validation helps businesses identify whether customer numbers are correctly formatted and suitable to use before sending messages or relying on them in important customer journeys.
How can businesses reduce failed customer contact?
Businesses can reduce failed customer contact by regularly checking customer phone data, validating numbers before use, removing duplicates, correcting formatting issues and verifying numbers before important communication journeys.